PRHT Powered Hard Top Strange intermittent fault buttons mixed up

Technical Area Electrics & ICE
1
  1. My model of MX-5 is: 2.0 NC Mk3 MX5 (manual 5 speed, PRHT)
  2. I’m based near: Calne, Wiltshire, UK
  3. I’m looking for technical help or recommendations on: Intermittent PRHT fault. Worked when I bought it, doesnt really work now. See below for details.

The problem:

On a flat surface, in neutral with engine running or with ignition on, PRHT does not retract reliably. I can undo the latch and the roof warning light to the left of the hazard light illuminates. Here is where it gets really odd; sometimes it is silent, sometimes an intermittent beep, sometimes it goes halfway and sometimes the buttons dot THE OPPOSITE to the action displayed on them!

I have managed to open and close the roof fully once today through button mashing, turning off, turning on, patting the roof firmly etc.

What have I done so far?:

I have read a lot of forum posts about broken limit switches, broken motors, poor engagement of gear teeth etc. There is no noise at all when the roof decides to work, no graunching, grinding or clicking… The limit switches seem fine, the warning buzzer clearly works, there is no water in the cabin or the ‘tray’ behind the seats where the roof tucks away. Also there is no physical impediment to its movement (cuddly toy, A-Z etc). The hinges look really well greased and when it chooses to move, it is smooth as silk.

I have disconnected battery for 30 mins. Clock cleared but radio didn’t ask for code, did I leave it long enough?

Battery voltage is 12.58v cold and once running it is charging beauifully (hopefully ruling out under and over voltage issues).

What do I think is wrong?:

I am stumped, that’s why I am here. Anyone seen the mixed button, intermittent PRHT roof problem before? Thanks in advance.

PS back into MX5 after a long hiatus. Sold a BMW 645 to buy this as I wanted to be more connected to the fun driving I do. It is definitely fun but currently isnt living up to the Which? survey suggesting it is the most reliable used car you can buy in the UK. I am not sulking or particularly cross, it is a relatively cheap used car, the weather isn’t scorching hot, the AC works, it drives beautifully, it is clean and well looked after, it is just the roof that is ‘showing off’.

2

Hmm, check for leaks from the scuttle grommets!

Rust tracks on the interior metalwork and fusebox behind the glovebox, and possibly also a damp passenger footwell. If left to fester this will become very expensive when other things go wrong as well.

Silicone sealant around the white plastic insert for the screw holding the scuttle panel is the cure. See the Downloads section on how to fix it.

Mine done five years ago.

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3

Richard, Lightning quick response. Cheers. Will get checking this eve if I have time. Has been very rainy so perhaps that explains it. Will report back with my findings…

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4

Richard is bang on with the fault diagnosis in my opinion.
There was a recent thread on hear with an owner experiencing very similar symptoms to you and it was the water ingress from memory.
It was dried out etc and all worked hunky dory.
Welcome and just up the road in BOA. :+1::slightly_smiling_face:

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5

Found it for you.

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Dear Pals,

I am watching THIS VIDEO which details not only how to do the job but also the telltales that it needs doing.

  1. rust dripping down under dash - I have this
  2. wet carpets (dont have this but maybe they are marginally moist).

Cheers,

F

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7

If the scuttle grommets haven’t been done they will need doing. It’s one of the MK3 jobs guaranteed to need attention.

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I am on the case now.

Thanks for the advice. I will be trying to do it this evening.

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9

Thread update:

I removed the cap and screw
Disconnected washer jet
Removed trim panel
Removed grommet with carpenters pincers
Cleaned grommet
Cleaned Hole
Put silicone down hole
Put silicone on grommet
Put grommet in
More silicone one top
Smoothed with wet finger
Put fan heater in pass footwell on low to dry fusebox

Let’s see what happens.

mx5001 mx5002 mx5003 mx5004 mx5005 mx5006 mx5007 mx5008

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10

I think there’s enough sealer on there…

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11

Better safe than sorry but I agree, probably a bit OTT!

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12

I don’t think you can use too much, as long as you got some underneath as well :+1:

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13

I stuffed tons everywhere.

14

Hope that works. Presume that you haven’t got the SmartTop module?

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That was my initial thought. Smart tops have been known to go silly.

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No paperwork on a smart top.

How do I spot one?

Cheers,

F

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The box is piggy backed with electrical connectors to the folding top control unit behind the passenger seat back bulkhead plastic cover

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If you are able to operate the roof while thecar is moving slowly then you have one.

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I previously said piggybacked but the smart top is actually in series.

20

That should fix it!

Have you done Drivers’ side? Less of a problem, but also necessary…